A method and a control system for exerting defined caliper clamping forces in a disk brake which can be actuated by means of an electric motor are known from the international patent application WO 05/100114. In that case the control system has a cascade structure consisting of three successive controllers, namely a first controller in the form of a force-travel controller, a second controller connected downstream of the first controller, in the form of a rotational speed controller, and a third controller, connected downstream of the second controller, in the form of a current controller. Only a clamping force reference value is supplied to the control system; that is to say that force control for adjusting this clamping force reference value is possible with the control system.
DE 103 02 515 A1 describes a device and a method for controlling the force and position of an electric brake system of a motor vehicle. The control system structure can be operated in two operating modes, force control or position control, transfer between the operating modes being effected by a switch whereby the position reference value for the engine controller is made available either by a force controller or by a further unit. The control system structure described therefore comprises, so to speak, two parallel units (force controller and further unit), only one of the two units being used for a prescribed operating mode.
It is therefore the object of the present invention to propose a method and a device for controlling a brake which can be actuated electrically by means of an actuator, which method and device can execute situation-adapted control using a unified, in particular simple, controller device.
This object is achieved by a method and device according to the invention.
The invention is based on the concept that the controller device includes, in addition to a predefined, unified controller structure to which a predefined type of controller structure input variables are supplied, a selection and evaluation device which determines the appropriate controller structure input variables from the input variables of the controller device, so that the controller device, despite having a permanently predefined controller structure, can execute at least two different control modes, such as force control or speed control or position control.
According to the invention the term actuator position is understood to mean, in addition to a position, for example the axial position of a spindle of the actuator, also an angle, for example the angle of a rotor of the actuator, or another variable-characterizing position.
An advantage of the invention is that, for the same functionality, the number of necessary controllers/units, and therefore the production costs, can be reduced, as compared to the known control system structures.
A further advantage of the invention lies in the unified, simple structure, resulting in simpler activation, for example when the controller device must be re-initialized.
Furthermore, as a result of the unified structure, switching between control modes is possible in a simple manner, without, for example, the need to execute switching processes in the controller itself. In this way the occurrence of undefined controller states is avoided.
Preferably, the controller device can be operated using the same controller structure in at least three control modes, force control or position control or speed control.
To make possible selection of the control modes, a control mode parameter, by which the control mode to be implemented by the controller device is determined, is preferably supplied as an input variable to the selection and evaluation device. The further input variables of the selection and evaluation device depend on the control mode parameter, at least one actuator actual value and at least one actuator reference value being made available to the selection and evaluation device. Especially preferably, actual values for the actuator clamping force and the actuator position are supplied to the selection and evaluation device independently of the control mode parameter, the selection and evaluation device using for evaluation only the actual value required for the control mode at the time.
According to a preferred embodiment of the invention, the controller structure includes at least one position controller and the selection and evaluation device makes available to the controller structure in each control mode an actuator position as a controller structure input reference value and controller structure input actual value.
According to an advantageous development of the invention, the controller structure includes a position controller, with a speed controller connected downstream of the position controller. An actuator speed reference value output by the position controller and the actuator speed actual value are then supplied as input variables to the speed controller. Especially preferably, the controller structure includes no further controller, so that the speed controller outputs the manipulated variable for the actuator. Advantageously, the position controller includes a speed limitation which limits the actuator speed reference value output by the position controller to a predefined maximum value in order to protect the actuator from damage.
In order to execute speed control, in accordance with a preferred embodiment of a method according to the invention a reference value for the actuator position is determined, in the selection and evaluation device, from the actuator clamping force reference value supplied to the selection and evaluation device with reference to a predefined relationship between actuator position and actuator clamping force, and an actual value for the actuator position is determined from the actuator clamping force actual value supplied to the selection and evaluation device. These determined reference and actual values for the actuator position are output to the position controller as controller structure input reference value and controller structure input actual value.
For rapid determination of the reference and actual values for the actuator position, the predetermined relationship between actuator position and actuator clamping force is preferably stored in the form of a table in the selection and evaluation device.
According to a further preferred embodiment of a method according to the invention, for speed control an actuator speed reference value and an actuator position actual value are supplied to the selection and evaluation device. In the selection and evaluation device a reference value for the actuator position is determined from the actuator speed reference value and is supplied to the position controller together with the actuator position actual value.
In the case of a speed controller connected downstream of the position controller, in a speed control operation the reference value for the actuator position is preferably determined from the actuator speed reference value, in the selection and evaluation device, in such a way that the actuator speed reference value output by the position controller corresponds to the actuator speed reference value which was supplied to the selection and evaluation device. A speed control operation can therefore be carried out by a predefined controller structure having an external position controller and an internal speed controller.
The controller device can preferably be operated in a control mode with relative position control. For this purpose a relative actuator position reference value reproducing a desired position change, and an actuator position actual value, are supplied to the selection and evaluation device. The selection and evaluation device determines by addition, from the relative actuator position reference value and an actuator position value stored prior to entering the relative position control mode, a reference value for the actuator position, which is output to the position controller together with the actuator position actual value.
Preferably, the controller device can be operated alternatively or additionally in a control mode with absolute position control, in which at least one actuator position reference value and an actuator position actual value are supplied to the selection and evaluation device, which values are supplied as controller structure input reference value and controller structure input actual value to the position controller of the controller structure.
According to a preferred embodiment of the invention, the control mode parameter and the at least one actuator reference value are supplied to the selection and evaluation device by a higher-level electronic control and regulation unit. Information and/or requests, for example regarding the driver braking wish, demands of a slip control system (ABS: antilock system, TCS: traction control system) or driver assistance system (ESC: electronic stability control), initialization request, request for brake lining clearance adjustment, are usually present at the higher-level electronic control and regulation unit, so that appropriate control of the brake can be decided in the higher-level electronic control and regulation unit and the corresponding actuator reference value is determined.
The invention also relates to an electronic brake system for a motor vehicle comprising at least one brake which can be actuated electrically by means of an actuator, and a control and regulation unit, the control and regulation unit having at least one device according to the invention or being connected to at least one device according to the invention.